System and method for automation of rotorcraft entry into autorotation and maintenance of stabilized autorotation

ABSTRACT

The system is configured for automation of rotorcraft entry into autorotation. The system can provide a means to assist the flight crew of a rotorcraft in maintaining rotor speed following loss of engine power. The system can automatically adjust control positions, actuator positions or both to prevent excessive loss of rotor speed upon initial loss of engine power before the flight crew is able to react. The system uses model matching to provide axis decoupling and yaw anticipation; it includes pitch control initially to assist in preventing rotor deceleration; and it makes use of collective, pitch, roll and yaw trim functions to provide tactile cueing to the pilot to assist when the pilot is in the loop. The system can reduce workload by assisting the crew with controlling rotor speed and forward speed during stabilized autorotation.

BACKGROUND

1. Technical Field

The present disclosure relates in general to a system and method offlight control of a rotorcraft. More specifically, the presentdisclosure relates to a system and method for automation of a rotorcraftentry into autorotation and maintenance of stabilized autorotation.

2. Description of Related Art

A traditional method of dealing with autorotation relies on pilotrecognition of the engine failure and subsequent pilot action to reducethe collective pitch rapidly in order to preserve main rotor RPM toallow for a controlled rate of descent and maintenance of sufficientrotor kinetic energy to slow the rate of descent prior to landing andcushion the landing. Also, pilot manipulation of the cyclic may berequired, depending on the aircraft dynamics and the flight condition,to initially maintain rotor speed and subsequently adjust forward speedfor maximum efficiency. Previous rotorcraft systems have used enginedata and rotor speed measurements to trigger warnings to assist theflight crew in recognizing the condition. Significant room forimprovement remains in the field of flight control systems forrotorcraft.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the system and method ofthe present disclosure are set forth in the appended claims. However,the system and method itself, as well as a preferred mode of use, andfurther objectives and advantages thereof, will best be understood byreference to the following detailed description when read in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a side view of a rotorcraft, according to an exampleembodiment of the present disclosure;

FIG. 2 is a schematic view of a system configured for automation of arotorcraft entry into autorotation and maintenance of stabilizedautorotation, according to an example embodiment of the presentdisclosure;

FIG. 3 is a schematic view of a method of automation of rotorcraft entryinto autorotation and maintenance of stabilized autorotation, accordingto an example embodiment of the present disclosure; and

FIG. 4 is a schematic view of a computer system, according to exampleembodiment of the present disclosure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the system and method of the presentdisclosure are described below. In the interest of clarity, all featuresof an actual implementation may not be described in this specification.It will of course be appreciated that in the development of any suchactual embodiment, numerous implementation-specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present disclosure, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the device described herein may beoriented in any desired direction.

Referring now to FIG. 1 in the drawings, a rotorcraft 101 isillustrated. Rotorcraft 101 has a rotor system 103 with a plurality ofrotor blades 105. The pitch of each rotor blade 105 can be managed inorder to selectively control direction, thrust, and lift of rotorcraft101. For example, a swashplate mechanism 123 can be used to collectivelyand/or cyclically change the pitch of rotor blades 105. Rotorcraft 101further includes a fuselage 107, anti-torque system 109, and anempennage 111. Torque is supplied to rotor system 103 and anti-torquesystem 109 with at least one engine 113. A main rotor transmission 115is operably associated with an engine main output driveshaft 121 and themain rotor mast. It should be appreciated that even though rotorcraft101 is depicted as having certain illustrated features, it should beappreciated that rotorcraft 101 can take on a variety of implementationspecific configurations, as one of ordinary skill in the art would fullyappreciate having the benefit of this disclosure.

System 201 is illustrated in conjunction with rotorcraft 101. It shouldbe appreciated that though system 201 is illustrated with regard torotorcraft 101, system 201 is equally implementable on other aircraft aswell. Further, it should be appreciated that system 201 can beimplemented in a wide variety of configurations, depending in part uponthe flight control configuration of the rotorcraft.

System 201 is configured for automation of rotorcraft 101 entry intoautorotation. System 201 provides a means to assist the flight crew of arotorcraft in maintaining rotor speed following loss of engine power.The system 201 can automatically adjust control positions, actuatorpositions or both to prevent excessive loss of rotor speed upon initialloss of engine power before the flight crew is able to react. System 201goes beyond the existing methods in that it makes use of the ability ofa full authority or properly equipped partial authority aircraft flightcontrol system (AFCS) to control the collective pitch of the rotordirectly with the swashplate actuators, providing a quicker responsethan utilizing a trim actuator alone; it uses model matching to provideaxis decoupling and yaw anticipation; it includes pitch controlinitially to assist in preventing rotor deceleration; and it can makeuse of collective, pitch, roll and yaw trim functions to provide tactilecueing to the pilot to assist when the pilot is in the loop. System 201can further reduce workload by assisting the flight crew withcontrolling rotor speed and forward speed during stabilizedautorotation. Another unique feature of system 201 is that it containslogic to recognize pilot intent based on input and allows the pilot theability to override the AFCS actions at any time during the loss ofengine power event.

System 201 can monitor engine status information, whether measureddirectly by the flight control system or received over an interface withthe engine system. Upon detection of a loss of engine power, system 201can manipulate the flight control actuation system, as required for theflight condition, to prevent potentially catastrophic loss of rotorkinetic energy. System 201 can tailor the control response to themeasured flight condition. System 201 can make use of all actuationmeans available to the flight control system to preserve rotor speed,including full authority direct automatic control of main rotorswashplate in pitch, roll and collective and tail rotor collective andhigh-rate or low-rate parallel actuators in the pitch, roll, collectiveand directional control axes. System 201 can simultaneously decreasecollective pitch and decrease anti-torque input without waiting for ayaw rate to develop. In other words, system 201 is configured toanticipate the decrease in anti-torque requirement when making adecrease in pitch angle of the rotor blades. If required due to highforward airspeed, system 201 can command an aft cyclic input to increaseflow through the rotor to prevent excessive loss of rotor RPM and toslow the aircraft toward the autorotation speed. Model-matchingtechniques can provide a much quicker response than simple proportionintegral derivative (PID) controllers used in conventional closed-loopsystems. If the flight condition is not appropriate for automaticcollective reduction (such as due to proximity to ground), or if thepilot attempts to override the automatic system, system 201 can allowthe pilot to control the aircraft and can provide tactile cueing toassist the pilot in retaining rotor speed. During continuedautorotation, the flight control system will use rotor actuation, trimand cueing systems to maintain a predefined rotor speed.

In another embodiment, system 201 is configured to provide cycliccontrol upon loss of the first engine on multi-engine aircraft whenoperating above the single-engine Vne. This assists the flight crew inquickly returning to the one engine inoperable (OEI) envelope, which iscritical should a second engine loss be experienced in rapid succession(fuel contamination, etc.).

System 201 provides a wider pilot recognition window following a loss ofpower than is provided without system 201. The time is valuable inpreventing excessive loss of rotor speed when engine loss occurs whilethe flight crew is occupied with other tasks, or during high workloaddue to multiple failure conditions. This is applicable to allrotorcraft, but is particularly valuable for rotorcraft with lowerinertia rotors. The system 201 also reduces pilot workload significantlyby providing multi-axis inputs during initial entry into autorotationand by providing automatic maintenance of rotor speed, forward speed andattitude throughout the autorotation event.

System 201 can provide a fully available protection system (if supportedby the flight control system architecture), and also can provide thecapability to tailor the response to the flight condition. System 201also can provide automatic detection of pilot overriding inputs andallows full control authority to the flight crew when desired. Theassistance with maintenance of stabilized autorotation improves safetyas the flight crew divides its attention between flying and non-flyingtasks while preparing for the subsequent emergency landing.

System 201 is configured to make use of the rotorcraft flight controlsystem to generate commands to the main rotor collective and cycliccontrol axes and tail rotor collective to assist the pilot inmaintaining sufficient rotor speed and aircraft control immediatelyfollowing loss of all engine power or loss of all remaining engine poweron single-engine or multi-engine helicopters. System 201 can beconfigured to make use of a full-authority Fly-By-Wire (FBW)architecture; a traditional mechanical control system architecture withlimited-authority series actuators, full-authority series actuators,low-rate parallel (trim) actuators or any combination of the above; or amechanical control system with high-rate parallel actuators. For aconventional control system, system 201 is unique in the use of seriesactuators (either high- or low-authority) in the collective axis. Incontrast, conventional systems have utilized low-rate parallel trimactuators in the collective axis.

System 201 can monitor flight conditions and tailor the responsefollowing the power loss to the existing flight conditions and powersettings. System 201 can reduce main rotor collective pitch, to preserveRPM and adjust tail rotor collective to compensate for decrease in antitorque requirement. Unlike conventional systems, system 201 can make useof direct control of the main rotor collective pitch to provide a morerapid response and tighter closed-loop control of rotor speed. Thishigh-rate control of collective pitch may be provided either inherentlyin a FBW architecture, through the addition of a high-authority orlow-authority series actuator in the collective axis in conventionalcontrol architectures or through the use of a high-rate parallelactuator. System 201 can monitor airspeed and, if required for enginefailure during high power and high airspeed conditions, can adjustlongitudinal cyclic to increase upward airflow through the main rotor,while simultaneously slowing the aircraft toward the autorotation speed.In the case of high power Out-of-Ground-Effect hover conditions, system201 can pitch the nose down to achieve airspeed suitable for safeautorotation.

System 201 can monitor other flight parameters and inhibits activationof the protection function when not required or when inappropriate (suchas when in a landing configuration). Once established in autorotation,system 201 can use collective pitch to maintain a predefined rotor speedand uses cyclic pitch to maintain the most efficient forward speed.System 201 can tailor the commanded response, including RPM, to theflight condition. System 201 can monitor pilot control input andestimate pilot intent to allow override capability, if required. Inaddition to direct control of the rotors, system 201 can provide tactilecueing in the collective, pitch and roll cyclic and pedal cockpitcontrol axes (if supported by the flight control system architecture) tohelp the pilot maneuver to and remain within the rotorcraft maneuveringenvelope appropriate to the flight condition. In an aircraft withconventional flight control system architecture with only a low-rateparallel trim actuator in the collective axis, system 201 is unique inthe use of tactile cueing to assist the pilot while in the loop.

System 201 can also provide the capability to assist the pilot throughautomatic control or control cueing in the collective, pitch, roll andyaw axes to maneuver to a point within the predefined single-enginemaneuvering envelope following loss of an engine in multi-enginerotorcraft. Such a feature can aid in mitigating the potential foraggravating an autorotation condition should loss of a subsequent enginefollow the initial engine loss during high power flight conditions. Thesystem 201 can be implemented through the use of conventional PIDmethods, model-matching methods or other optimal or robust controltechniques.

Referring also to FIG. 2, system 201 is illustrated in conjunction withvarious rotorcraft components. System 201 is operable with one or moreengines 113 that are mechanically coupled to a tail rotor transmission125 and main rotor transmission 115. The pitch of tail rotor blades 129can be collectively changed by a tail rotor actuator 127. The pitch ofmain rotor blades 105 can be collectively and/or cyclically changed byswashplate mechanism 123. Engines 113 can be controlled by enginecontrol computers 131 that are in communication with one or more flightcontrol computers 133. Flight control computers 133 can take on a widevariety of operational responsibilities. For example, in a fly-by-wireflight control system, flight control computers 133 can analyze pilotinputs and make corresponding commands to engine control computers 131,tail rotor actuator 127, and swashplate mechanism 123. Further, flightcontrol computers 133 are configured to make tactile cueing commands topilot controls and receive input commands from pilot controls, such as acollective stick 137, with a collective force feel/trim actuator 139.Aircraft state sensors 135 are in communication with flight controlcomputers 133. Illustrative aircraft state sensors 135 can include anyvariety of sensors configured for measure any variety of rotorcraftsystems and rotorcraft environment. For example, aircraft state sensors135 can includes sensors for measuring: air density, altitude, attitudeorientation, yaw orientation, temperature, airspeed, and acceleration,to name a few examples.

System 201 can include software and/or hardware for performing anyfunctionality described herein. For example, system 201 can be embodiedpartially or wholly within one or more modules within flight controlcomputers 133. Further, system 201 can include any variety of computersystems, as discussed further herein with regard to FIG. 4.

Referring now also to FIG. 3, a method 301 for automation of arotorcraft entry into autorotation and maintenance of stabilizedautorotation is schematically illustrated. Method 301 can include a step303 of recognizing and confirming an engine failure. In the case of asingle engine rotorcraft, step 303 includes recognizing and confirmingthe loss of power of the single engine. In the case of a multi-enginerotorcraft, step 303 includes recognizing and confirming the loss ofpower of the multiple engines. The recognition of the engine failure canbe performed by engine control computers 131 or by independent sensorsthat measure one or more functions engines 113. The confirmation of theengine failure can be performed by recognizing a droop or decrease inrotor speed, which acts as a failsafe so that subsequent steps of method301 are not inadvertently performed. It should be appreciated thatconfirmation of engine failure can be performed by other methods otherthan recognizing a decrease in rotor speed, for example, an enginetorque sensor can be utilized to provide engine failure confirmation.

Method 301 can further include a step 305 of analyzing the flightcondition of rotorcraft 101. Step 305 can include processing data fromaircraft state sensors 135 so that subsequent actuations of main rotorblades 105 and tail rotor blades 129 take into account the operationalstate of the aircraft.

Method 301 can further include a step 307 of actuating swashplatemechanism 123. Step 307 can also include actuating tail rotor actuator127 to collectively change the pitch of tail rotor blades 129 in orderto compensate to a decrease in the pitch of main rotor blades 105 thatcan result in a decrease in required tail rotor thrust. Step 307includes collectively reducing the pitch of main rotor blades 105 by theflight control computers 133 by making a direct command to the actuatorsconnected to swashplate mechanism 123. The action of making a directcommand from flight control computers 133 to the actuators connected toswashplate mechanism 123 increases efficiency and reduces the timerequired to have an effect on preservation of the rotor speed necessaryto achieve an effective autorotation. The degree or amount of decreasein main rotor blade pitch can be initially made and continuously changedin order to achieve and regulate a desired RPM of rotor blades 105,thus, RPM data is continuously being received and processed by flightcontrol computers 133, which thereby makes pitch change commands to theactuators connected to swashplate mechanism 123. The actuation ofswashplate mechanism 123 can also entail making a cyclic change to thepitch of main rotor blades 105 in order to cause the rotorcraft to havea desired pitch attitude, which can have a positive effect on airflow upthrough the rotor disc. For example, a nose up angle of approximately 15degrees can promote airflow up through the rotor disc, which can have apositive effect on preservation of rotor speed. The cyclic change to thepitch of main rotor blades 105 can be analyzed and commanded by flightcontrol computer 133 which are in communication with aircraft statesensors 135, such as pitch attitude sensors.

Method 301 can include a step 309 that includes activating a tactilecueing to one or more pilot controls. Step 309 can be implementedsimultaneous or subsequent to step 307. The tactile cueing in step 309can include actuation of trim actuator 139 to move collective stick 137to mimic the pitch changes automatically occurring in main rotor blades105 by flight control computers 133.

Steps 305 through 309 can be implemented in a recurring loop such thatsteps 305 through 309 are recurring so as to continuously achieve adesired RPM of rotor blades 105. In an alternative embodiment of method301, step 307 includes changing the pitch of main rotor blades 105 thatwill predicatively achieve a target value RPM of rotor blades 105. Thepredictive algorithm controls collective pitch as a function of flightcondition. The algorithm provides for maintenance of RPM immediatelyfollowing the engine failure and during subsequent changes in flightcondition, such as when maneuvering to the proper stabilizedautorotation and during the landing flare. Such an embodiment of method301 can result in a quicker and/or smoother achievement of RPMpreservation because the system isn't chasing the desired RPM of rotorblades 105 that could result in a high frequency oscillatory change inrotor blade pitch. The target value of collective pitch position ofrotor blades 105 can be chosen by flight control computer 133 that has alook-up table containing desired collective pitch values required toachieve the desired RPM based on flight condition and pilot input. Inaddition, the target value RPM of rotor blades 105 may be chosen byflight control computer 133 that has a look up table containing desiredrotor RPM's for a variety of aircraft states.

System 201 is configured such that the pilot can override the automaticrotor blade pitch changes being implemented in method 301 at any time.Further, system 201 can be configured such that intervention by thepilot only temporarily halts method 301 so that steps 305-309 areautomatically performed again after lack of pilot inputs for a period oftime. The intervention by the pilot can be implemented simply by thepilot overriding the controls, thus the pilot's causing desired rotorblade control, for example.

Method 301 can also include one or more steps for automating a flareportion of the autorotation procedure. Such steps can include ananalysis by flight control computer 133 concluding that the aircraft iswithin close proximity to the ground so as to automatically increase thepitch of rotor blades 105. Further, system 201 can also be configuredsuch that intervention of method 301 by the pilot below a certainaltitude permanently halts the reoccurrence of steps 305-309 becausesystem 201 determines that the pilot is intervening to perform the flareportion of the autorotation.

Referring now also to FIG. 4, a computer system 401 is schematicallyillustrated. Computer system 401 can be configured for performing one ormore functions with regard to the operation of system 201 and method301, further disclosed herein. Further, any processing and analysis canbe partly or fully performed by computer system 401. Computer system 401can be partly or fully integrated with other aircraft computer systems.

The system 401 can include an input/output (I/O) interface 403, ananalysis engine 405, and a database 407. Alternative embodiments cancombine or distribute the input/output (I/O) interface 403, analysisengine 405, and database 407, as desired. Embodiments of the system 401can include one or more computers that include one or more processorsand memories configured for performing tasks described herein. This caninclude, for example, a computer having a central processing unit (CPU)and non-volatile memory that stores software instructions forinstructing the CPU to perform at least some of the tasks describedherein. This can also include, for example, two or more computers thatare in communication via a computer network, where one or more of thecomputers include a CPU and non-volatile memory, and one or more of thecomputer's non-volatile memory stores software instructions forinstructing any of the CPU(s) to perform any of the tasks describedherein. Thus, while the exemplary embodiment is described in terms of adiscrete machine, it should be appreciated that this description isnon-limiting, and that the present description applies equally tonumerous other arrangements involving one or more machines performingtasks distributed in any way among the one or more machines. It shouldalso be appreciated that such machines need not be dedicated toperforming tasks described herein, but instead can be multi-purposemachines, for example computer workstations, that are suitable for alsoperforming other tasks.

The I/O interface 403 can provide a communication link between externalusers, systems, and data sources and components of the system 401. TheI/O interface 403 can be configured for allowing one or more users toinput information to the system 401 via any known input device. Examplescan include a keyboard, mouse, touch screen, and/or any other desiredinput device. The I/O interface 403 can be configured for allowing oneor more users to receive information output from the system 401 via anyknown output device. Examples can include a display monitor, a printer,cockpit display, and/or any other desired output device. The I/Ointerface 403 can be configured for allowing other systems tocommunicate with the system 401. For example, the I/O interface 403 canallow one or more remote computer(s) to access information, inputinformation, and/or remotely instruct the system 401 to perform one ormore of the tasks described herein. The I/O interface 403 can beconfigured for allowing communication with one or more remote datasources. For example, the I/O interface 403 can allow one or more remotedata source(s) to access information, input information, and/or remotelyinstruct the system 401 to perform one or more of the tasks describedherein.

The database 407 provides persistent data storage for system 401. Whilethe term “database” is primarily used, a memory or other suitable datastorage arrangement may provide the functionality of the database 407.In alternative embodiments, the database 407 can be integral to orseparate from the system 401 and can operate on one or more computers.The database 407 preferably provides non-volatile data storage for anyinformation suitable to support the operation of system 201 and method301, including various types of data discussed further herein. Theanalysis engine 405 can include various combinations of one or moreprocessors, memories, and software components.

The particular embodiments disclosed herein are illustrative only, asthe system and method may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Modifications, additions, or omissionsmay be made to the system described herein without departing from thescope of the invention. The components of the system may be integratedor separated. Moreover, the operations of the system may be performed bymore, fewer, or other components.

Furthermore, no limitations are intended to the details of constructionor design herein shown, other than as described in the claims below. Itis therefore evident that the particular embodiments disclosed above maybe altered or modified and all such variations are considered within thescope and spirit of the disclosure. Accordingly, the protection soughtherein is as set forth in the claims below.

To aid the Patent Office, and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims to invokeparagraph 6 of 35 U.S.C. §112 as it exists on the date of filing hereofunless the words “means for” or “step for” are explicitly used in theparticular claim.

The invention claimed is:
 1. A method of automating an autorotation inan aircraft, the method comprising: recognizing a failure of an engine;analyzing a flight condition of the aircraft; actuating a swashplatemechanism with a direct command from a flight control computer to anactuator coupled to the swashplate mechanism so as to change a pitch ofa plurality of main rotor blades to a predetermined collective pitchvalue, the predetermined collective pitch value being chosen by theflight control computer referring to a look-up table containing desiredcollective pitch values for a variety of aircraft flight conditions; andtemporarily pausing the step of actuating the swashplate for a period oftime after a pilot has made an overriding command.
 2. The methodaccording to claim 1, further comprising: confirming the failure of theengine.
 3. The method according to claim 1, further comprising:confirming the failure of the engine by detecting a decrease in rotorspeed of the plurality of main rotor blades.
 4. The method according toclaim 1, further comprising: calculating a desired rotor speed of themain rotor blades based in part upon the step of analyzing the flightcondition of the aircraft.
 5. The method according to claim 4, whereinthe step of actuating the swashplate mechanism includes changing thepitch of the plurality of main rotor blades to obtain the desired rotorspeed.
 6. The method according to claim 1, further comprising:commanding an actuation of a tail rotor actuator with the flight controlcomputer in order to change a pitch of a plurality of tail rotor bladesin order to correlate a change in a tail rotor thrust requirementbecause of a change in pitch of the plurality of main rotor blades. 7.The method according to claim 1, further comprising: actuating acollective stick with a trim actuator to cue a pilot when the flightcontrol computer has commanded the change to the pitch of the pluralityof main rotor blades.
 8. The method according to claim 1, wherein thestep of actuating the swashplate mechanism with the command from aflight control computer to an actuator coupled to the swashplatemechanism so as to change the pitch of a plurality of main rotor bladesincludes collectively decreasing the pitch of the plurality of mainrotor blades.
 9. The method according to claim 1, wherein the step ofactuating the swashplate mechanism with the command from a flightcontrol computer to an actuator coupled to the swashplate mechanism soas to change the pitch of a plurality of main rotor blades includescyclically changing the pitch of the plurality of main rotor blades toincrease an attitude of the aircraft so as to promote an airflow upthrough the plurality of main rotor blades.
 10. The method according toclaim 1, further comprising: actuating a swashplate mechanism with aflare command from the flight control computer to the actuator coupledto the swashplate mechanism so as to increase the pitch of the pluralityof main rotor blades upon detection that the aircraft is at apredetermined distance from a ground surface.